Four more lawmen were wounded in the bloodbath and a cache of weapons was seized, including a single AK-47 assault rifle that authorities say was purchased 800 miles (1,300 kilometers) away at a Phoenix gun shop and smuggled into Mexico.

The rifle's presence in Mexico underscores two realities in the government's war against drug traffickers: Nearly all the guns the cartels use are smuggled into Mexico from the U.S., and officials say a small number of corrupt American weapons dealers are making the gun running possible.

"It's a war," said Bill Newell, special agent in charge of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives in Arizona and New Mexico. "It's a war between the drug cartels. And it's a war between the government and the drug cartels. And the weapons of war are the weapons that they are acquiring illegally here in the United States."

Gun running on the rise
Authorities don't know how many firearms are sneaked across the border, but the ATF says more than 7,700 guns sold in America were traced to Mexico last year, up from 3,300 the year before and about 2,100 in 2006. The increase is attributed both to a higher volume going south and a growing interest among Mexican authorities in running recovered weapons through a U.S. gun-tracing database.

Mexican and U.S. officials estimate the cartels get 95 percent of their guns from the United States; others are stolen when cartels overrun Mexican authorities. Cartels recruit "straw buyers" in the United States who make purchases on their behalf. Then people are paid to bring the weapons across the border.

U.S. Customs and Border Protection, whose inspectors scrutinize border-crossers at ports of entry, declined to characterize the frequency of its searches of vehicles driving into Mexico, but conceded that not all traffic leaving America is searched.

Inspections of vehicles coming into the United States are considered a bigger priority, because they are aimed at stopping weapons, terrorists and other dangerous elements from coming into the country. Periodic searches of outgoing traffic are done as spot checks and in response to tips of upcoming attempts to smuggle guns or cash.

"We just don't have the manpower to do 100 percent inspections of outgoing traffic," said agency spokesman Jason Ciliberti.

Federal agents say the small number of dealers who knowingly sell guns to smuggling rings have the potential to inflict a lot of damage. As evidence, they cite the Arizona gun dealer accused of selling the AK-47 recovered at the May 27 shootout in Culiacan involving the powerful Sinaloa cartel.

George Iknadosian, owner of X-Caliber Guns in Phoenix, is accused of selling guns to two groups of straw buyers when he knew the weapons were going to be smuggled into Mexico. He also was targeted in stings in which he allegedly sold guns to undercover officers posing as straw buyers.

Investigators believe 600 guns sold by Iknadosian ended up in Mexico, most headed to the violent Pacific Coast state of Sinaloa.

Authorities say several have surfaced. They include:

An AK-47 and .38-caliber Super pistol with diamond-encrusted grips found after the Nov. 2 killing of the police chief of the northern state of Sonora as he walked into a hotel about two miles south of the Arizona border.

A .38-caliber Super pistol seized a year ago when Mexican special forces captured a top Sinaloa cartel lieutenant, Alfredo Beltran Leyva, and three members of his security team in Culiacan.

Three assault rifles recovered after patrolling federal police officers were fired upon and responded by killing four gunmen from the Beltran Leyva drug gang on July 2 at a house in Culiacan.

Gunds traced to border states
The overwhelming majority of guns recovered in Mexico come from America's four southern border states, with Texas first, followed by California, Arizona and New Mexico, according to the ATF. Many of the rest come from other Western states (Washington, Nevada, Colorado and Oklahoma), the South (Georgia, Florida and Louisiana) and the Midwest (Illinois, Ohio and Indiana).

Gun smuggling corridors are usually dictated by proximity to the nearest and easiest sources of weapons.

Drug smugglers seek out guns in America because gun laws in Mexico are more restrictive than in the United States. Mexicans must get approval for a gun purchase from the Mexican defense department and are limited to guns with a caliber no higher than the standard .38-caliber. Larger calibers are considered military weapons and are off-limits to civilians.

Gun traffickers break caches into small loads to lower the risk of losing them all in a bust. Some guns are walked into Mexico, but most are driven through ports of entry, stuffed inside spare ties, fastened to undercarriages with zip ties, kept in hidden compartments, or bubble-wrapped and tucked in vehicle panels.

Investigators say smugglers sometimes wait until inspectors on both sides are busy with peak border traffic to drive across.

Smuggling adviser?
Prosecutors allege Iknadosian offered smuggling advice to a confidential informant during a police sting at his shop in Phoenix, telling the informant to break up purchases. "If you got pulled over two is no biggie," Iknadosian is quoted as saying in a search-warrant affidavit. "Four is a question. Fifteen is what are you doing. So if you got two, hey me and a buddy are going to go out shooting."

Arturo Sarukhan, the Mexican ambassador to the United States, says his country wants the U.S. government to fully enforce gun exportation laws, crack down on more straw buys at guns shows and gather more information on which firearms dealers are selling to rings.

For its part, Mexico must put more money and people into searching incoming border traffic, Sarukhan said.

"If Mexico and the United States are going to be successful, we are going to have to tango together," Sarukhan said.

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